Charged particle beam systems are conventionally used for material analysis. One method of material analysis using a charged particle beam system includes recording microscopic images of a sample by detecting secondary electrons or backscattered electrons generated by an electron beam scanned across a surface of the sample. An analysis of the recorded images provides, for example, information on the morphology of the sample. Another method of material analysis using a charged particle beam system includes detecting x-rays generated by a particle beam incident on the sample. An analysis of the detected x-rays may provide information on the elemental composition of the sample.
A material present at a given location on a sample can be identified by using a charged particle beam system to direct an electron beam onto the given location on a sample, and the x-ray spectroscopy system is used to detect a spectrum of x-rays coming from the sample in response to the electron beam directed onto the sample. The x-ray spectrum is analyzed in order to identify the material which is present at the location where the electron beam is incident on the sample. Such analysis is called “energy dispersive x-ray analysis” or “EDS”. The electron beam causes electrons from inner shells of the atoms of the material to be ejected, and electrons from outer shells drop to the inner shells and emit x-rays having an energy corresponding to the energy difference between the outer and inner electron shells of the atom. These x-rays are detected by the x-ray spectroscopy system. Since each chemical element has a unique atomic structure, the chemical element can be identified by an analysis of its x-ray spectrum. In particular, an element contained in the sample can be identified by its characteristic lines in the x-ray spectrum or by characteristic energies in the x-ray spectrum.
EDS analysis can be used, for example, to analyze samples from mines to determine the presence of valuable minerals, and decisions on the viability of a mine may be influenced by the EDS analysis. A high accuracy of the identification of minerals based on the EDS analysis is desired, accordingly. The material analysis may use a library of known materials, and an x-ray spectrum obtained from a given location on a sample can be compared with data stored in the material library in order to identify the material present at the location where the x-ray spectrum is generated. This usually works quite well in practice and allows to identify the materials present at many locations of arbitrary samples. However, it may occur that an x-ray spectrum recorded for a particular location does not match with one of the materials stored in the material library. It is then not possible to assign one of the known materials to this location of the sample, resulting in a lack of information which could be useful for the complete analysis of the sample.